Knee replacement surgery is one of the most commons surgical procedures to date performed at more than a million patients every year worldwide. The most common reason for performing a knee replacement surgery is that the patient suffers from knee joint osteoarthritis, which is a syndrome in which a low-grade inflammation results in pain in the joints. The low-grade inflammation is caused by abnormal wearing of the cartilage that covers and acts as a cushion inside joints, which results in a decrease of the synovial fluid that lubricates the knee joint.
In conventional surgery the surgeon places a prosthesis on the lateral condyle, the medial condyle or both the medial and the lateral condyle. The prosthesis could further more comprise a contacting surface placed on the top part of the tibia bone and an artificial part replacing the knee cap.
The procedure usually takes up to two hours and the surgeon will make a single cut (10 to 30 cm long) down the front of the knee. The kneecap is moved to one side to reach the knee joint. The worn or damaged surfaces are removed and the bone are shaped to fit the artificial knee joint.
The average patient age is between 65 and 75. Of these surgeries, approximately 80% are unilateral (only one knee replaced) and 20% are bilateral.
The knee joint comprises proximal contacting surfaces, being sections of the medial condyle, the lateral condyle and an area of the femoral bone between the medial and the lateral condyle and a distal contacting surface being a cross-section of the proximal part of the tibia bone. Furthermore the knee joint comprises the patella which is a, triangular bone which articulates with the femur and covers and protect the knee joint. The knee joint also comprises the minisci which are cartilaginous elements within the knee joint which serve to protect the ends of the bones from rubbing on each other. The minisci also acts as shock absorbers in the knee. There are two menisci in each knee, the medial meniscus and the lateral meniscus.
Osteoarthritis is a common condition of cartilage failure that can lead to limited range of motion, bone damage and invariably, pain. Due to a combination of acute stress and chronic fatigue, osteoarthritis directly manifests itself in a wearing away of the articulating surface and, in extreme cases, bone can be exposed in the joint. Some additional examples of cartilage failure mechanisms include cellular matrix linkage rupture, chondrocyte protein synthesis inhibition, and chondrocyte apoptosis.